Concanavalin-mediated attachment to membranes of a cellular slime mould cyclic AMP phosphodiesterase

In the cellular slime mould Dictyostelium, a membrane-bound cyclic AMP phosphodiesterase undergoes a tenfold increase in activity when amoebae reach the aggregation stage of development. Our previous studies had shown that when non-aggregating cells, which produce extracellular and intracellular forms of the enzyme, are treated with the lectin Concanavalin A (Con A), they exhibit prematurely high levels of the membrane bound enzyme. The present results indicate that this effect may be largely due not to the induction of the enzyme by Con A but rather to the binding of the intracellular form of the enzyme to membranes by Con A. This conclusion is based on the findings that: a) the enzyme activity associated with membranes from Con A treated cells can be decreased by treatment with the haptenic sugar alpha-methyl mannoside: b) mambranes from untreated cells having only low membrane-bound phosphodiesterase activity can acquire increased activity after incubation with Con A and intracellular phosphodiesterase; c) the intracellular phosphodiesterase binds to Sepharose-Con A and is eluted with alpha-methyl mannoside. These results raise the possibility that some of the effects attributed to Con A in the literature may not be due directly to Con A but to glycoproteins attached to membranes by Con A.